The present invention relates to semiconductor devices such as heterojunction bipolar transistors, surface emitting laser diodes and hetero-insulated gate field effect transistors; and the fabrication method thereof.
In a prior art semiconductor device, for example, in a heterojunction bipolar transistor using III-V compound semiconductors, as shown in FIG. 3, an oxygen ion-implanted region 13 (hereinafter, referred to as "extrinsic collector region") is formed under an extrinsic base region 5 composed of a single crystalline compound semiconductor, so that carriers in the region 13 are depleted to reduce the extrinsic base-collector capacitance, thus achieving the high speed operation of the heterojunction bipolar transistor. In FIG. 3, reference numeral 1 indicates a single crystalline semiconductor substrate; 2 is a heavily doped n-type GaAs layer; 3 is an n-type GaAs layer; 7 is an undoped GaAs layer; 8 is an n-type AlGaAs layer; 9 is a heavily doped n-type GaAs layer, 10 is an emitter electrode; 11 is a base electrode; and 12 is a collector electrode. Such a technique has been disclosed, for example, in IEEE Electron Device Letters EDL-5 (1984) pp. 310-312.
In a prior art surface emitting laser diode, as shown in FIG. 51, at a p-type Bragg reflection layer 34, an oxygen ion-implanted region 39 is formed under a beryllium ion-implanted region 40 composed of a single crystalline compound semiconductor to obtain a current-confinement structure, thus improving the device characteristics. In FIG. 51, reference numeral 31 indicates a heavily doped n-type GaAs substrate; 32 is an n-type Bragg reflection layer; 33 is an InGaAs strained quantum well layer (active layer); 35 is an Al.sub.2 O.sub.3 film; 37 is a p-type electrode; 38 is an n-type electrode; 39 is an oxygen ion-implanted region; and 4 is a SiO.sub.2 film. Such a technique has been disclosed, for example, in Applied Physics Letters 56 (1990) pp. 1942-1944.
In a prior art hetero-insulated gate field effect transistor (hereinafter, referred to as "HBT"), as a gate electrode 6 shown in FIG. 56, a film made from a metal or a metal-semiconductor compound, for example, tungsten or WSi (tungsten silicide) is used. In FIG. 56, reference numeral 1 indicates a single crystalline semiconductor substrate; 5 is a heavily doped p-type GaAs layer; 35 is an Al.sub.2 O.sub.3 film; 41 is a p-type GaAs channel layer; and 42 is an undoped AlGaAs layer. Such a technique has been disclosed in Unexamined Japanese Patent Publication No. HEI 1-161874.
In the prior art HBT described above, as shown in FIG. 3, as the extrinsic base region 5, the single crystalline compound semiconductor is used to reduce the resistance. The extrinsic base region 5 is formed on the extrinsic collector region 13 (collector under the base electrode 11) made from a single crystalline compound semiconductor by an epitaxial growth method. However, since the extrinsic collector region 13 is made from a compound semiconductor having a large relative dielectric constant (for example, about 13 for GaAs), and accordingly, in the HBT made from a III-V compound, it is difficult to further reduce the extrinsic base-collector capacitance.
In the prior art HBT described above, the area of the emitter region 8 cannot be made smaller than that of the emitter electrode 10, which makes it difficult to decrease the size of the HBT and to further reduce the extrinsic base-collector capacitance.
In the prior art surface emitting laser diode described above, a leak current is generated due to the crystal defect resulting from the oxygen ion implantation, which obstructs the formation of the perfect current-confinement structure. This brings about such a disadvantage that the device characteristics are not desirable, or rather liable to be deteriorated.
In the prior art hetero-insulated gate field effect transistor described above, since the surface of the semiconductor barrier layer is exposed in atmospheric air when the gate electrode is formed, the density of interface states at the metal-semiconductor interface is varied depending on the device fabricating condition, that is, cannot be made constant. As a result, the device characteristics are varied, which causes such a disadvantage in making it impossible to obtain the field effect transistors having the uniform characteristics.
Further, since metals are difficult to be processed as compared with semiconductors, when a gate electrode is made from a metal, the metal electrode length is determined by the dimension with which the metal is processed. This makes it difficult it to decrease the device size and to improve the integration density.